Systems exist that assemble microchips automatically based upon some sort of encoding such as electrostatic or magnetic coding. The system uses the encoding to identify and position the microchips as part of the assembly process.
Examples of these systems can be found in U.S. Pat. No. 7,861,405, and its related cases, US Patent Publications 20100192365, 20100186221, and 20100186222, owned by the assignee of this application. Another example is shown in U.S. Pat. No. 7,332,361, that teaches charge-encoded elements having basic or acidic surfaces capable of carrying charge in non-polar liquids with charge control agents. Examples include two-particle electrophoretic ink, liquid toner, inorganic oxides and polymers. Standard photolithography or ink-jet technology can be used to pattern these materials to form charge-encoded elements. All of these references are incorporated by reference here. The system uses a charge or magnetic polarity on the chip to sort and position the microchips.
These references make general mention of possible methods of how chips have the charge or polarity, but give no details. For example, issues can arise with the deposition of the charge or polarity. Currently, no current technique exists to deposit a charge pattern on isolated microchips. One approach has charged one end of a nanowire, another has charged up one side of a symmetric microchip, but no work appears to be done on isolated microchips or charge patterning.
The fabrication process should be compatible with existing devices on the chips. In addition, the process should not increase the manufacturing costs, but still allow the patterning on a scalable level between larger areas and small features. In order to provide a flexible system, the system should allow for varying magnitudes of charge density, and ideally but not necessarily, both positive and negative polarity, for multiple levels of chip control and identification. The charge patterns should have good stability to allow long shelf life of the patterned devices.
Another issue with patterning may arise with the chips being attracted to each other. They may gather together or conglomerate based upon their respective charges. The density of the chips needs to remain low enough the chips do not exchange charge by contact with each other.